The Obama campaign didn't fight hard in many of the Congressional districts colored red. Only in Pennsylvania, Ohio, Missouri and West Virginia do you seem much red in a state contested by Obama. But look at two other states with overwhelmingly white regions that gave Clinton over 70% of the primary vote but where Obama improved on John Kerry's performance. In the Appalachian regions of Virginia and North Carolina, it's clear that the hard work of the Obama campaign paid off.

Speaking of Silver, Nate says it's not a matter of vote percentage, it's a matter of white vote percewntage, and all-white Appalachia does better than the Deep South:

The Appalachian counties don't stand out in this map. McCain did extremely well among whites in a much broader area in the southeast, with the Appalachian counties standing out in the earlier map only because they had very few black votes to cancel out the swing among the whites. Actually it looks like McCain did even better in some of the counties just south of that Appalachian belt.